#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	int a, b = 0;
	double sum = 0.0;
	double sum1 = 0.0;
	double sum2 = 0.0;
	for (a = 1; a <= 99; a+=2)
	{
		sum1 += 1.0 / a;
	}
	for (b = 2; b <= 100; b += 2)
	{
		sum2 += 1.0 / b;
	}
	sum = sum1 - sum2;
	printf("%lf", sum);
	return 0;
}